The present invention relates generally to the field of telephones for use in telephone systems, more particularly to improving the serviceability of such telephones, and especially to ways of preventing the out-of-order status and consequent loss of incoming-call service whenever such telephones are inadvertently left off-hook.
Present-day telephones, whether of the traditional electromechanical sort or the more recently introduced electronic type, must be placed in an on-hook status in order to be able to receive an incoming call. That is, the voice network used during telephone conversation must be disconnected from the telephone lines such that the ringer circuit can respond to a ring signal by alerting the user either aurally or, sometimes, visually.
Such an on-hook status is traditionaly established by placing the telephone handset on a cradle when not in use. The cradle incorporates a switch which senses the presence of the handset and responds by disconnecting the voice network from the telephone lines. More recently introduced telephones often achieve the same on-hook status when the handset is laid down on a flat surface, or by some other manual means of operating the hookswitch to disconnect the voice network from the phone lines.
However, there are many instances when the telephone may be inadvertently left off-hook, resulting in the phone being placed in an out-of-order status as to incoming calls until the user discovers the problem and hangs up the telephone. Such instances occur frequently when young children or pets play with or jostle the telephone, when the user is called away from the telephone while waiting in a hold status and forgets to return, or simply when the phone is carelessly and improperly hung up such that the hookswitch fails to be actuated.
The problem of the off-hook telephone is familar to the companies which supply telephone service. In most localities supplied by such service, an off-hook alert signal in the form of a distinct audio tone or a set of audio tones is transmitted to a telephone left off-hook for a period of time without any user activity such as dialing or connection and conversation. This signal is fairly loud and is usually cycled on and off or warbled in frequency or volume such that a user who is nearby will hear it and be alerted to hang up the telephone.
However, the alert signal is usually terminated after a short period of time and the off-hook telephone is then silent. If the off-hook alert signal is transmitted at a time when the user is not near enough to the phone to hear it, or at a time when other environmental noises render the alert signal inaudible, the telephone can remain out of order for a long period of time.
Consequently, some other means for restoring service to a phone left off-hook would be highly desirable since it would make the phone more dependable. Considerable improvement in this regard would result from the provision of a signalling device which provides a more readily sensible signal indicating inadvertent off-hook status, such as a louder alarm, perhaps in combination with a flashing light. However, it would be preferable to automatically restore service to an off-hook phone without undue delay instead of merely attempting to alert the user to hang up the phone. Whatever means of coping with inadvertent off-hook status is chosen should be inexpensive to produce, capable of working with an existing phone or of incorporation into a new telephone design, and completely reliable.